# Adolescent circadian phase shifts: novel time-of-day targets for bright light

> **NIH NIH R01** · RUSH UNIVERSITY MEDICAL CENTER · 2023 · $502,048

## Abstract

PROJECT SUMMARY
A majority of older adolescents in the U.S. are chronically sleep deprived, getting 1- 2 h less sleep than
recommended. The circadian (~24-h) system shifts later (delay) with the progression of puberty; this shift
contributes to late sleep onsets in older adolescents. Early school start times force teenagers awake earlier
than their spontaneous wake time. Thus, the opportunity for sleep shortens. Many adolescents are also
waking for school at the “wrong” circadian time. Chronic circadian misalignment and sleep restriction are at
their peak during late adolescence, and are associated with morning daytime sleepiness, poor academic
performance, conduct problems, depressed mood, suicidal ideation, substance use, insulin resistance, and
obesity. Bright light exposure from light boxes can shift rhythms earlier (phase advance) to facilitate earlier
sleep onset, and reduce morning circadian misalignment and the associated risks. We constructed the first
phase response curves (PRCs) to bright light in older adolescents. To phase advance circadian rhythms, our
PRCs showed that the ideal time to begin light exposure was slightly before wake-up time and light should be
avoided around bedtime because this is when light produces maximum phase delay shifts. An unexpected
finding from our results, however, was a second advancing region in the afternoon (~6 to 9 h after habitual
wake-up time) suggesting that afternoon light may have more circadian phase advancing ability than
traditionally thought. The overall goal of this mechanistic study is to follow-up on our unexpected PRC findings
and test whether individually-timed afternoon light alone and in combination with morning bright light can shift
circadian rhythms earlier in older adolescents aged 14 to 17 years. Four groups will be compared in a
randomized parallel group design: afternoon bright light, morning bright light, morning + afternoon bright light,
and a dim room light control. Adolescents will complete a 2-week protocol. After a baseline week with a stable
sleep schedule, adolescents will live in our laboratory for 4 days. Sleep/dark and the time of bright light
exposure will gradually shift earlier. Bright light (~5000 lux) will be timed individually based on his/her stable
baseline sleep schedule. The first 3-h morning bright light exposure will begin 1 h before wake on the first
morning. The first 3-h afternoon bright light exposure will begin 6 h after wake. The morning + afternoon
exposures will begin at the same times, but each exposure will be 1.5 h so that a total of 3 h of bright light per
day will be given to each group except the dim light control group. Phase shifts of the circadian clocks marked
by the dim light melatonin onset (DLMO) is the main outcome. We hypothesize that afternoon bright light will
advance DLMO more than dim room light and afternoon bright light will work synergistically with morning bright
light to produce larger shifts than morning or afternoon brigh...

## Key facts

- **NIH application ID:** 10684645
- **Project number:** 5R01HL151512-04
- **Recipient organization:** RUSH UNIVERSITY MEDICAL CENTER
- **Principal Investigator:** Stephanie Crowley McWilliam
- **Activity code:** R01 (R01, R21, SBIR, etc.)
- **Funding institute:** NIH
- **Fiscal year:** 2023
- **Award amount:** $502,048
- **Award type:** 5
- **Project period:** 2020-08-01 → 2025-06-30

## Primary source

NIH RePORTER: https://reporter.nih.gov/project-details/10684645

## Citation

> US National Institutes of Health, RePORTER application 10684645, Adolescent circadian phase shifts: novel time-of-day targets for bright light (5R01HL151512-04). Retrieved via AI Analytics 2026-05-23 from https://api.ai-analytics.org/grant/nih/10684645. Licensed CC0.

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